1. Field of the Invention
The present invention relates to a pressure container for filling up various kinds of compressed gas such as a compressed natural gas (CNG) and the like, various kinds of liquefied gas such as a liquefied natural gas (LNG), a liquefied petroleum gas (LPG) and the like, and the other various kinds of pressurizing materials.
2. Description of the Related Art
There has been conventionally known a pressure container 50 for the CNG in which a metal mouth piece 52 is mounted to a polyethylene liner 51 which does not transmit the CNG and outer peripheries of the liner 51 and the mouth piece 52 are coated with an FRP reinforcing layer 53 which satisfies a predetermined pressure resistance standard, as shown in FIG. 7. In the pressure container 50, since a main body portion is kept in an air tight state by the synthetic resin liner 51, there is an advantage that a weight of a vehicle can be reduced in the case of being used as a fuel tank or the like for an automotive vehicle. Further, in order to keep the mouth piece mounting portion in an air tight state, the structure is made such that a coating portion 51a for coating the mouth piece 52 from an inner side is provided in the liner 51, thereby pressure contacting the coating portion 51a to an inner surface of a boss portion 52a and a flange portion 52b in the mouth piece 52 by a gas pressure.
However, a coefficient of thermal expansion is greater in the polyethylene liner 51 than the metal mouth piece 52, so that the polyethylene liner 51 is contracted and expanded in accordance with a change of temperature in a relatively greater manner. Accordingly, for example, as shown in FIG. 8, the liner 51 is contracted at a low temperature, the coating portion 51a is peeled from the mouth piece 52 and a gap 54 is generated between the both, thereby causing a poor seal. Further, there is a case that a crack is generated in the coating portion 51a due to a residual stress caused by a contraction of the liner 51 at a time of forming and a repeated stress caused by a contraction and expansion of the liner 51 in accordance with a change of temperature. As mentioned above, it is not said that the conventional pressure container 50 is perfect in a reliability of an airtight seal in a bonding portion between the liner 51 and the mouth piece 52.